Biaxially oriented multilayer polymer tube for medical devices

ABSTRACT

A tubular extruded member particularly suitable for use in medical devices such as intravascular catheters and guide wires, wherein the extruded tubular member includes multiple layers having biaxial helical orientation in different directions. A counter-rotation extrusion process may be used to orient the layers in different biaxial helical directions. The counter-rotation extrusion process provides orientation in two different circumferential directions in addition to a longitudinal direction. By combining the dual direction or biaxial helical orientation with multiple layers, different layers of the tubular member may be tailored to have the desired mechanical properties.

RELATED APPLICATIONS

[0001] This application is related to co-pending patent application Ser.No. ______ filed on even date herewith, entitled MEDICAL DEVICE WITHEXTRUDED MEMBER HAVING HELICAL ORIENTATION (attorney docket1001.1468101), the entire disclosure of which is hereby incorporated byreference.

FIELD OF THE INVENTION

[0002] The present invention generally relates to extruded polymertubular members for medical devices. More specifically, the presentinvention relates to extruded polymer tubular members for medicaldevices having helical orientation.

BACKGROUND OF THE INVENTION

[0003] A wide variety of medical devices utilized extruded polymericmembers. For example, intravascular catheters and guide wires commonlyutilize an extruded polymeric tube as a shaft component. Becauseintravascular catheters and guide wires must exhibit good torqueability,trackability and pushability, it is desirable that the extrudedpolymeric shaft component have good torque transmission, flexibility andcolumn strength. These attributes are commonly incorporated intointravascular catheters by utilizing a composite shaft construction.Alternatively, the polymer material which forms the extruded polymericshaft component may be oriented to enhance the mechanicalcharacteristics thereof.

[0004] For example, U.S. Pat. No. 5,951,494 to Wang et al. discloses avariety of medical instruments, such as guide wires and catheters,formed at least in part of elongated polymer members having helicalorientation. The helical orientation is established by post-processingan extruded elongate polymer member with tension, heat and twisting.Wang et al. theorize that the tension, heat and twisting process resultsin a polymer member that has helical orientation on the molecular level.Such molecular helical orientation enhances torque transmission of theelongate polymer member, which is important for some types ofintravascular medical devices to navigate through tortuous vascularpathways.

[0005] U.S. Pat. No. 5,059,375 to Lindsay discloses an extrusion processfor producing flexible kink resistant tubing having one or morespirally-reinforced sections. The extruder includes a rotatable memberhaving an extrusion passageway for spirally extruding a thermoplasticfilament into a base thermoplastic material to form a tube. Therotatable member is rotated to form the reinforcement filament in aspiral or helical pattern in the wall of the tubing.

[0006] U.S. Pat. No. 5,639,409 to Van Muiden discloses an extrusionprocess for manufacturing a tube-like extrusion profile by conveying anumber of divided streams of material of at least two differentcompositions through a rotating molding nozzle. The streams of materialflow together in the rotating molding nozzle to form at least twohelically shaped bands of material. After allowing the combined streamsof material to cool off, an extrusion profile comprising a plurality ofbands of material extending in a helical pattern is formed.

[0007] U.S. Pat. No. 5,248,305 to Zdrahala discloses a method ofmanufacturing extruded catheters and other flexible plastic tubing withimproved rotational and/or longitudinal stiffness. The tubing comprisesa polymer material including liquid crystal polymer (LCP) fibrilsextruded through a tube extrusion die while rotating the inner and outerdie walls to provide circumferential shear to the extruded tube.Rotation of the inner and outer die walls orients the LCP in a helicalmanner to provide improved properties, including greater rotationalstiffness.

[0008] Although each of these prior art methods provide some degree oforientation which enhances the mechanical characteristics of extrudedpolymeric members, there is an ongoing need to further enhance themechanical characteristics of medical devices such as intravascularcatheters and guide wires to improve performance thereof.

SUMMARY OF THE INVENTION

[0009] The present invention provides a tubular extruded memberparticularly suitable for use in medical devices such as intravascularcatheters and guide wires, wherein the extruded tubular member includesmultiple layers having biaxial helical orientation in differentdirections. A counter-rotation extrusion process may be used to orientthe layers in different helical directions. The counter-rotationextrusion process provides orientation in two different circumferentialdirections in addition to a longitudinal direction. By combining thedual direction helical orientation with multiple layers, differentlayers of the tubular member may be tailored to have the desiredmechanical properties. Thus, for example, to increase torquetransmission of an intravascular guide wire, the outer layer may beformed of a relatively rigid material. To increase column strengthand/or kink resistance of an intravascular catheter, the inner layer maybe formed of a relatively soft and flexible material. To increase burststrength of an intravascular balloon, the inner layer may incorporate arelatively hard and thin material. To increase puncture resistance of anintravascular balloon, the outer layer may be formed of a relativelysoft and durable material. In each instance, the multi-layer tubeincorporates biaxial helical orientation in different directions toenhance the mechanical properties thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a plan view of a multi-layered extruded tube inaccordance with an embodiment of the present invention;

[0011]FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1;

[0012]FIG. 3 is a plan view of an intravascular balloon catheterincorporating the tubular member illustrated in FIG. 1;

[0013]FIG. 4 is a schematic illustration of an extrusion process formanufacturing the tubular member illustrated in FIG. 1; and

[0014]FIG. 5 is a schematic illustration of an alternative manufacturingprocess for manufacturing the tubular member illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The following detailed description should be read with referenceto the drawings in which similar elements in different drawings arenumbered the same. The drawings, which are not necessarily to scale,depict illustrative embodiments and are not intended to limit the scopeof the invention.

[0016] Refer now to FIG. 1 which illustrates a tubular polymer extrudedmember 10 in accordance with the present invention. Extruded tubularpolymer member 10 includes a plurality of coaxial tubular layers 12/14and a lumen 16 as best seen in FIG. 2, which is a cross-sectional viewtaken along line 2-2 in FIG. 1. For purposes of illustration only, thetubular member 10 is shown to include two layers, namely an inner layer12 and an outer layer 14. It is to be understood, however, that thetubular member 10 may incorporate virtually any number of concentrictubular layers, depending on the desired characteristics of the tubularmember 10.

[0017] The tubular member 10 has orientation in two differentcircumferential directions as indicated by reference lines 22 and 24.Reference line 22 illustrates the helical orientation of the innertubular layer 12 and reference line 24 illustrates the helicalorientation of outer layer 14. Reference line 26 shown in FIG. 2illustrates the different rotational directions of the biaxial helicalorientation. In this particular example, reference line 26 illustratesclockwise rotational orientation in the outer layer 14 andcounter-clockwise rotational orientation in the inner layer 12. It is tobe understood that the rotational orientation may be reversed. Inparticular, the outer layer 14 may have counter-clockwise rotationalorientation and the inner layer 12 may have clockwise rotationalorientation.

[0018] By combining the dual direction or biaxial helical orientationwith multiple layers 12/14, different layers of the tubular member 10may be tailored to have the desired mechanical properties. For example,the outer layer 14 may include a helically oriented relatively rigidmaterial to increase torsional rigidity. Alternatively, the inner layer12 may include a helically oriented relatively rigid material toincrease hoop strength (i.e., burst strength). As a further alternative,the inner layer 12 may include a helically oriented relatively flexiblematerial to increase kink resistance. As yet a further alternative, theouter layer 14 may include a helically oriented relatively durablematerial to increase puncture resistance. These and other examples oftubular member 10 are particularly useful when incorporated into amedical device such as catheter 30 described with reference to FIG. 3.

[0019]FIG. 3 illustrates an intravascular balloon catheter 30, which issubstantially conventional with the exception of incorporating one ormore of the several embodiments of the tubular member 10 described withreference to FIG. 1. The intravascular balloon catheter 30 includes anelongate shaft 32 having a proximal end and a distal end. A conventionalmanifold 34 is connected to the proximal end of the elongate shaft 32.An inflatable balloon 36 is connected to the distal end of the elongateshaft 32. The elongate shaft 32 may be formed at least in part of themulti-layer tube 10 described with reference to FIGS. 1 and 2. Inaddition, the balloon 36 may be formed at least in part from ablow-molded multi-layer tube 10.

[0020] As mentioned previously, providing a multi-layer tube 10 allowseach of the individual layers 12/14 to be tailored with the desiredfeatures. For example, the inner layer 12 may be formed of a relativelyhard and rigid polymeric material. Concentrating the relatively hard andrigid polymeric material in the inner layer 12 increases hoop strength(i.e., burst strength) and improves kink resistance of the tubularmember 10. Providing a catheter 30 having a shaft 32 and a balloon 36that is able to withstand high inflation pressures is advantageous forcertain clinical applications requiring high inflation pressure.Providing a catheter 30 having a shaft 32 that is kink resistant isadvantageous because damage due to handling and/or navigation throughtortuous vasculature is mitigated.

[0021] Alternatively, the inner layer 12 may be formed of a relativelysoft and flexible polymeric material. Concentrating the relatively softand flexible polymeric material in the inner layer 12 improves kinkresistance of the tubular member 10 if the outer layer 14 is formed of amaterial susceptible to kinking. As mentioned above, providing acatheter 30 having a shaft 32 that is kink resistant is advantageousbecause damage due to handling and/or navigation through tortuousvasculature is mitigated.

[0022] The outer layer 14 may comprise a relatively hard and rigidpolymeric material. Concentrating the relatively hard and rigidpolymeric material in the outer layer 14 increases rotational stiffnessand column strength of the tubular member 10. Providing an intravascularguide wire having a shaft with increased rotational stiffness isadvantageous in clinical applications requiring 1:1 torque response forprecise steering, particularly in tortuous vasculature. In addition,providing an intravascular guide wire and/or catheter 30 having a shaft32 with increased column strength is advantageous in clinicalapplications requiring substantial longitudinal force transmission overlong distances as is usually required to cross tight vascularrestrictions.

[0023] Alternatively, the outer layer 14 may be formed of a relativelysoft and flexible polymeric material. Concentrating a relatively softand flexible polymeric material in the outer layer 14 improves thedurability of the tubular member 10. Providing a catheter 30 having aballoon 36 with increased durability mitigates the likelihood of balloonburst due to puncture from a calcified vascular deposit or from a stent.

[0024] When utilized to form a portion of the elongate shaft 32, themulti-layer tube 10 may have a wall thickness ranging from approximately0.002 inches to 0.010 inches, and a length ranging from 10 cm to 150 cm.When utilized to form the balloon 36, the multi-layer tube 10 may have awall thickness (post blow-molding) ranging from 0.0005 inches to 0.002inches, and a length ranging from 1 cm to 10 cm. These dimensions areprovided by way of example, not limitation.

[0025] The relative thickness and material composition of each layer12/14 may be modified to balance the respective properties of theelongate shaft 32 or balloon 36. For example, the thickness of the innerand outer layers of 12/14 may be modified and/or the materials selectedfor the inner and outer layers 12/14 may be modified.

[0026] Examples of suitable rigid polymers include polyurethane(isoplastic), aromatic polyamide, polyamide, PET, PEN, LCP,polycarbonate, aromatic polyester, etc. Examples of suitable soft andflexible polymers include polyurethane elastamers, polyether blockamides (PEBA), Pellethane, Hytrel, Arnitel, Estane, Pebax, Grilamid,Vestamid, Riteflex, etc.

[0027] A specific example of a hard-soft multiple-layer combination isone layer formed of a polyamide (e.g., nylon or PEBA) and another layerformed of polyethylene with a tie-layer of polyethylene copolymerdisposed therebetween. Another specific example of a hard-softmultiple-layer combination is one layer formed of aromatic nylon and theother layer formed of nylon 12.

[0028] The inner and/or outer layers 12/14 may also comprise areinforced polymer structure such as a polymer layer includingcontinuous liquid crystal polymer fibers (LCP) dispersed in a non-LCPthermal plastic polymer matrix. The LCP content of the LCP containinglayer may be greater than 0.1% by weight and less than 90% by weight. Inaddition, for enhanced performance, the LCP containing layer maycomprise 0.05% to 50% by weight of the combined layers.

[0029] Refer now to FIG. 4 which illustrates an extrusion system 100 formanufacturing the multi-layer tubular member 10 discussed with referenceto FIGS. 1 and 2. Extrusion system 100 includes one or more extruders50A/50B coupled to an extrusion head 40 as schematically illustrated byextrusion lines 60. Each extruder 50A/50B includes a hopper 52, a heatedbarrel 56, an extrusion screw 58, and a control system 54. The controlsystem 54 of each extruder 50A/50B is operably coupled as indicated bydashed line 51 to facilitate co-extrusion.

[0030] Extrusion head 40 includes an outer die portion 42 having a fixedportion 42F and a rotatable portion 42R. Extrusion head 40 furtherincludes a rotatable pin 44 rotatably disposed in the outer die portions42F and 42R. Molten polymer enters the extrusion head 40 at inlets 48Aand 48B. The molten polymer entering inlet 48A forms the inner layer 12and the molten polymer entering inlet 48B forms the outer layer 14 ofthe multi-layer extrusion 10. The molten polymer flows through theextrusion passages as indicated by the small arrows. The molten polymerexits the extrusion head 40 through outlet 46. Upon exiting theextrusion head 40 through outlet 46, the molten polymer begins tosolidify to form the multi-layer tube 10 which may be subsequently cutto length or taken up by spool 80.

[0031] The rotatable pin 44 is coupled to a rotational drive 70A whichrotates in the direction indicated by arrow 76A. The rotational drive70A may comprise, for example, a motor 72 coupled to the rotational pin44 by a chain or belt 74. Similarly, the rotational outer die 42R isconnected to rotational drive 70B which rotates in the directionindicated by arrow 76B. Note that the direction of rotation of drive 70Ais different than the rotational direction of drive 70B, therebyrotating the pin 44 in a different direction than the outer die 42R.

[0032] As the molten polymer exits the extrusion head 40 through outlet46, the rotatable outer die imparts helical orientation to the outerlayer 14 of the tubular member 10. In addition, as the molten polymerexits the outlet 46 of the extrusion head 40, the rotating pin 44imparts helical orientation to the inner layer 12 of the tubular member10. Because the pin 44 is rotated in the opposite direction of rotatableouter die 42R, the helical orientation imparted to the outer layer 14 isin the opposite direction of the helical orientation imparted to theinner layer 12. Although not shown, an air passage may extend throughthe pin 44, which may be used to pump air into the tubular member 10 asit solidifies to help maintain the lumen 16 therein. As the moltenpolymer begins to solidify after exiting through outlet 46, the biaxialhelical orientation imparted to the inner and outer layers 12/14 islocked into the tubular member 10.

[0033] Refer now to FIG. 5 which illustrates an alternative extrusionsystem 200 for manufacturing the multi-layer tubular member 10. Exceptas described herein, the extrusion system 200 is similar to theextrusion systems described in co-pending patent application ______filed on even date herwith, entitled MEDICAL DEVICE WITH EXTRUDED MEMBERHAVING HELICAL ORIENTATION, the entire disclosure of which is herebyincorporated by reference.

[0034] Extrusion system 200 includes two or more extruders 50A/50Bcoupled to extrusion head 40 substantially as described previously.However, in this embodiment, the pin 44 remains stationary and is hollowto serve as a guide for mandrel 90. Molten polymer enters the extrusionhead 40 at inlets 48A/48B and flows through the extrusion passages asindicated by the small arrows. The molten polymer exits the extrusionhead 40 through outlet 46. Upon exiting the extrusion head 40 throughoutlet 46, the molten polymer begins to solidify thereby creating asemi-molten polymer state. In a semi-molten state, the polymer typicallyhas a temperature below the melting point but at or above the glasstransition point.

[0035] In this semi-molten state, the multi-layer tubular member 10 isrotated by rotational drive 70C in a direction indicated by arrow 76C.The support mandrel 90 is also rotated by a rotational drive 70A in adirection indicated by arrow 76A. The support mandrel 90 and themulti-layered tubular member 10 are rotated in the same direction, whilethe rotational outer die 42R is rotated in the opposite direction byrotational drive 70B as indicated by arrow 76B.

[0036] By rotating the multi-layer tubular member 10 in the semi-moltenstate, a molecular helical orientation is imparted to both the innerlayer 12 and the outer layer 14. In particular, in the semi-moltenstate, the crystalline regions of the polymer are helically oriented byrotation and subsequently allowed to cool thereby locking in the biaxialhelical orientation on the molecular level. Helical orientation is alsoimparted to the outer tubular layer 14 in the opposite direction byvirtue of the rotating outer die 42R. The multi-layer tubular member 10may be cut into discrete lengths immediately after extrusion or spooledonto take-up spool 80A. If the multi-layer tubular member 10 is taken-upby spool 80A, the multi-layer tubular member 10 and the spool 80A may berotated simultaneously. Similarly, if the support mandrel 90 is providedon a spool 80B, the spool 80B and the support mandrel 90 may be rotatedsimultaneously.

[0037] A further alternative extrusion system for manufacturing themulti-layer tubular member 10 is partially disclosed in U.S. Pat. No.5,622,665 to Wang, the entire disclosure of which is hereby incorporatedby reference. Wang '665 discloses a method for making differentialstiffness tubing for medical products, such as catheters. The methodproduces a tubing that has a stiff section and a flexible section joinedby a relatively short transition section in which the materials of thestiff and flexible sections are wedged into each other in a smoothgradual manner to produce an inseparable bond between the materialswithout abrupt joints. The method also employs a resin modulating systemthat minimizes the length of the transition section by minimizing thevolumes in all flow channels of the co-extrusion head used to producethe tubing.

[0038] Wang '665 further discloses a system for co-extrudingdifferential stiffness tubing. The system includes a co-extrusion headinto which extruders feed the different resins, such as a soft resin anda stiff resin, that will be used to form the finished tubing. Amodulating device regulates the flow of the resins from each of theextruders into the co-extrusion head, while another modulator may beused to bleed resin “A” from the head to relieve residual pressure. Toproduce tubing with differential stiffness, the modulators are actuatedperiodically and in synchronized fashion to abruptly stop or change theresin flow to the head. Because of the design of co-extrusion head, theinterface between the stiff resin and soft resin is naturally shearedand elongated when flowing through the flow channels of the head. Thus,these abrupt changes or stoppages by the modulators result in a verygradual change of stiff layer thickness in the tubing, creating thegradual stiffness change of the tubing. After discharge from the head,the tubing is cooled by passage through a water tank to form the tubing.

[0039] The system disclosed by Wang '665 may be modified for purposes ofthe present invention. In particular, as with the extrusion systemdiscussed with reference to FIG. 4 of the present application, arotational drive may be coupled to the pin in the co-extrusion head ofWang '665, and a rotational drive may be coupled to the die of Wang'665, with the necessary modifications made to the co-extrusion head topermit such rotation. The rotational drives may comprise, for example, amotor coupled to the pin and die by a chain or belt. The direction ofrotation of the pin drive is different than the rotational direction ofthe die drive, thereby rotating the pin in a different direction thanthe die.

[0040] As the molten polymer exits the modified co-extrusion head ofWang '665, the rotatable die imparts helical orientation to the outerlayer 14 of the tubular member 10 and the rotatable pin imparts helicalorientation to the inner layer 12 in the opposite direction. Althoughnot shown, an air passage may extend through the pin 44, which may beused to pump air into the tubular member 10 as it solidifies to helpmaintain the lumen 16 therein. As the molten polymer begins to solidifyafter exiting through the modified extrusion head of Wang '665, thebiaxial helical orientation imparted to the inner and outer layers 12/14is locked into the tubular member 10.

[0041] Those skilled in the art will recognize that the presentinvention may be manifested in a variety of forms other than thespecific embodiments described and contemplated herein. Accordingly,departures in form and detail may be made without departing from thescope and spirit of the present invention as described in the appendedclaims.

What is claimed is:
 1. A medical device comprising an extruded tubularpolymer member, the tubular polymer member having an inner tubular layerand an outer tubular layer, wherein the inner tubular layer has helicalorientation in a first direction and the outer tubular layer has helicalorientation in a second direction different from the first direction. 2.A medical device as in claim 1, wherein the tubular polymer member ismade by an extrusion process including the step of extruding the polymermember through a rotating extrusion head over a counter-rotatingmandrel.
 3. A medical device as in claim 1, wherein the tubular polymermember is made by an extrusion process including the step of rotatingthe polymer member after passing through a counter-rotating extrusionhead.
 4. A medical device as in claim 1, wherein one of the inner andouter tubular layers is formed of a relatively flexible polymericmaterial and the other of the inner and outer tubular layers is formedof a relatively rigid polymeric material.
 5. A medical device as inclaim 1, wherein one of the inner and outer tubular layers is formed ofcontinuous LCP fibers dispersed in a non-LCP polymer matrix.
 6. Amedical device as in claim 5, wherein the LCP content of the LCPcontaining layer is between 0.1% and 90% by weight.
 7. A medical deviceas in claim 5, wherein the LCP containing layer comprises 0.05% to 50%by weight of the combined layers.
 8. A medical device comprising anextruded tubular polymer member formed of a relatively rigid polymerictubular layer and a relatively flexible polymeric tubular layer, whereinthe relatively rigid polymeric tubular layer has helical orientation ina first direction and the relatively flexible polymeric tubular layerhas helical orientation in a second direction different from the firstdirection.
 9. A medical device as in claim 8, wherein the helicalorientation is formed by an extrusion process including the step ofextruding the polymer member through a rotating extrusion head over acounter-rotating mandrel.
 10. A medical device as in claim 8, whereinthe helical orientation is formed by an extrusion process including thestep of rotating the polymer member after passing through acounter-rotating extrusion head.
 11. A medical device comprising anextruded tubular polymer member, the tubular polymer member comprising afirst extruded tubular polymer layer and a second extruded tubularpolymer layer, the first extruded tubular polymer layer includingcontinuous LCP fibers dispersed in a non-LCP thermoplastic polymermatrix, wherein the first extruded polymer layer has helical orientationin a first direction and the second extruded polymer layer has helicalorientation in a second direction different from the first direction.12. A medical device as in claim 11, wherein the helical orientation isformed by an extrusion process including the step of extruding thepolymer member through a rotating extrusion head over a counter-rotatingmandrel.
 13. A medical device as in claim 11, wherein the helicalorientation is formed by an extrusion process including the step ofrotating the polymer member after passing through a counter-rotatingextrusion head.
 14. A medical device as in claim 11, wherein the LCPcontent of the LCP containing layer is between 0.1% and 90% by weight.15. A medical device as in claim 11, wherein the LCP containing layercomprises 0.5% to 50% by weight of the combined layers.
 16. A method ofmaking a medical tubular polymer member by rotating the polymer memberafter passing through a counter-rotating extrusion head.
 17. Anintravascular catheter including a shaft comprising a tubular polymermember formed by the method of claim
 16. 18. An intravascular catheterincluding an inflatable balloon comprising a tubular polymer memberformed by the method of claim 16.